1. Field of the Invention
The present invention relates to a method of beneficiating chromite ores by froth flotation. More particularly, the present invention involves the froth flotation of chromite ores with an amine flotation reagent.
2. Description of the Prior Art
Because chromium ore is a strategic mineral, substantial interest is involved in practical methods of extracting chromium ore values from domestic chromium ore sources. There are two general types of methods for separating chromium ore (chromite) values from associated gangue minerals by froth flotation techniques. In the first method chromite ore which has been deslimed is subjected to flotation at a pH of 1.5 to 5.5 with a long chain fatty acid collector as shown in U.S. Pat. No. 2,412,217. The selectivity of the process is enhanced by the inclusion of a soluble fluoride ion containing compound such as hydrofluoric acid, sodium fluoride or sodium silicofluoride in the flotation medium. The flotation process is typically conducted by adding 0.5 to 5.0 pounds fatty acid, 0.1 to 10.0 pounds soluble fluoride ion and 1.0 to 11.0 pounds sulfuric acid per ton of ore to the aqueous treatment medium containing the chromite ore. A typical product obtained by such a process from an ore containing 25.2% Cr.sub.2 O.sub.3 is a recleaner concentrate containing 41.0% Cr.sub.2 O.sub.3 and 2.5% SiO.sub.2 with a chromium recovery of 77.0%. In the second technique as shown in U.S. Pat. No. 3,473,656 chromite ore flotation is achieved with an undeslimed ore at a pH of 11.5 using a long chain fatty acid collector. The pH of the pulp is adjusted with NaOH with the pulp being dispersed by sodium silicate using carboxymethylcellulose as a flocculating depressant for silicate gangue minerals. Typically during processing, three pounds of sodium silicate, from 1.0 to 3.0 pounds of tall oil and from 0.25 to 0.50 pounds of carboxymethylcellulose per ton of ore, are added to a processing solution. From an ore containing 18.13% Cr.sub.2 O.sub.3 and 23.98% SiO.sub.2, a flotation concentrate was obtained containing 52.16% Cr.sub.2 O.sub.3 and 3.72% SiO.sub.2 with a chromium recovery of 80.0%. However, the conventional flotation methods involving fatty acid collectors have had a number of disadvantages among which is the relative poor selectivity of the flotation processes. Because of the selectivity problems, selectivity assisting reagents have had to be used in these processes. Fatty acid collectors are also very sensitive to slimes generated during aqueous beneficiation so that the ore must be thoroughly deslimed before flotation can be accomplished. Even with efficient desliming of the ore, however, the fatty acid flotation methods are characterized by substantial reagent consumption which adversely affects the economics of such processes. Moreover, all of the fatty acid methods require the use of silicate depressants such as soluble fluoride containing compounds, starches and the like, to increase selectivity. However, the use of fluoride ion containing compounds is unacceptable environmentally. Fatty acid chromite ore flotation techniques are also characterized by a very high reagent consumption which gives rise to unfavorable process economics. The interaction between fatty acid collectors and depressants for siliceous gangue is such that control of the flotation process is somewhat difficult.
Some attempts have been made for alternative methods of beneficiating chromite ores such as by amine flotation. In one such method as disclosed by S. Sobieraj et al. in Inst. Min. Metall., Trans. Sect. C, 1973 82 (December) 207, 13 chromite ore containing serpentine and olivine is subjected to flotation at an initial pH of 12.0 with an amine collector for the removal of serpentine followed by flotation of chromite at a pH of 3.0 with the same amine collector. Experimentation showed the best acting amine collectors to be amines with carbon chain lengths of 8 to 10. In a typical procedure 0.8 pound of amine collector is added to the flotation step, while 0.6 pound of amine collector is added to the flotation medium per ton of ore in the serpentine flotation step, while 0.6 pound of amine collector is added to the medium in the chromite flotation step. From an ore containing 36.0% Cr.sub.2 O.sub.3, a flotation concentrate was obtained containing 45.4% Cr.sub.2 O.sub.3 representing a chromium recovery of 87.0%. Assessment of the purity of the concentrate is impossible because no corresponding silicate content is shown. A need therefore continues to exist for an improved method of flotation of chromite ore which leads to greater efficiency of chromite ore extraction and less consumption of process reagents.